Sound rerecording system



Aug. 26, 1941. FLETCHER 2,254,034

SOUND RERECORDING SYSTEM Filed April 5, 1940 AMI/.9

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IN l/E N TOR By H. FLETCHER A TTORNEV r mnants-reign j v.

umrso -s ATEs "PATENT orrlcs assure SOUND BEBEOOBDING SYSTEM. Harvey Fletcher, Flushing, N. Y., assignor to Dell 1 Telephone Laboratories,

Incorporated, New

York, N. 1., a corporation of New York Ap ummn April 5, 1940, Serial No. 32am 1 s cum. (t1. fill-100.1)

This invention relates to sound rerecording systems and particularly to systems for rerecording volume compressed records.

Bound recording systems are known in which the volume range of the original sound is reduced or compressed and a separate record is made of the degree of compression. This separate record of the degree of compression, which may be recorded as a shown in United States Patent 1.623.756. April 5, 1927, C. F. Sacia, or as a modulated carrier current as shown in United States Patent 2,069, 810, February 9, 193?. H. D. Arnold. The object of the present invention is, during rerecording,.to arbitrarily vary the volume level of the rerecorded currents so as to enhance the volume contrast in the reproduced music.

A feature of the invention is, during rerecording to arbitrarily vary the rerecorded control current, in such manner as will result in a depansion of the volume range, and also to control the arbitrary volume level about which this expension takes place.

attenuator I is limited by the characteristics -01 conveniently be called a control record, may

slowly varying direct current, as-

The amount of arbitrary enhancement of the volume range afforded by manipulation of the the compressor used in the channel which produced the original record I, and the characteristics of theexp'ander which will be used in the channel used for the reproduction of the rerecorded record 5, this expander preferably having the same characteristics as the expander l0. As I .a control current is used for the control of the compressors, andexpanders. the degree of compression in the compressed range may be substantially complete, as shown in United States Patent 1,623,756 to Sacia. The compression and expansion need not be used throughout the whole range of volume recorded, that is, the lower sired'variation of the volume of the reproduced sound without impairing the function of the control current to restore the original volume variation in the sounds The drawing shows in rerecording system including one embodiment of the invention. The compressed sound is reproduced from the record I by the pick-up device I and, after suit- 'able amplification, in the amplifier 3, is rerecorded by the recorder l on the recording medium I. If desired, adjustable frequency discriminative networks may be associated with the amplifier 3 in the usual manner to modify the frequency pattern of the rerecorded sound. The

pick-up device 2 is of any suitable design adaptedfor reproducing the record on the record material I.

The control record, on the record material I,

. is reproduced by the pick-up device 8 and, if

desired, amplified in the amplifier After amplification, the control currents are supplied through the variable attenuator 8 to the recorder v I and are recorded on the recording material 5. Theattenuator l is shown as a balanced variable resistance network, but any other form of attenua'tor or potentiometer may be used as desired. A portion of the'signal currents in the output of the amplifier 3 are supplied to the expander II and, after suitable amplification in the amplifier ll,""are reproduced by the moni-' toring reproducer II. The control currents in the output of the attenuator 8 are also supplied tothe expander It to control the automatic ex- I '25 diagrammatic form a volume levels may be rerecorded and reproduced without compression and expansion, only the higher levels of volume being compressed in order to prevent overloading of the recording. device. However, no matter what type of compression and expansion is used, the expander l0, and the expander used in the reproducing channel, must have a range of expansion larger than the range used in compression, that is, the range used in compression plus the variation imposed on the control current by .the attenuator 8, mustnot exceed the available range of expansion in the expander ill, or in the expander in the reproducing channel. In a typical embodiment of the invention, compression is applied to the 'upper thirty decibels of the volume range and compresses this range into a range of some ten decibels on the original record. The compressor in the recording channel thus operates over a range of thirty decibels. The expander Ill, and the expander in the reproducing channel operate over an expanded range of fifty decibels. Thus the manipulation of the attentuator 8 can shift the operating range of the expander l0, ten decibels above or below normal without interfering in any way with the automatic expansion of the .volume range. While only a single rerecording channel has having a record of electrical waves compressed as to volume range and a control record of the degree of compression applied to the waves during recording, means for reproducing and rerecording said record of electrical waves, means energized by said reproduced wave for audibiy reproducing said electrical waves, means for reproducing and rerecording said control record and for controlling said audible reproduction and a manually variable attenuator in the channel for rerecording said control record.

2. In a rerecording system, a record of waves modified in amplitude, a record of the modifications made in the amplitudes of said waves, a pick-up for said record of modified waves, a recorder associated with said pick-up, a pick-up for said record of modifications, a recorder associated with said latter pick-up, and a manually variable attenuator in the circuit connecting said latter pick-up and said associated recorder.

3. The method oi! enhancing the amplitude of reproduced waves which comprises recording the waves modified in amplitude, recording the modiflcations made in the amplitudes of said waves, rerecording the record of said waves, rerecording said modifications, arbitrarily changing the magnitude of said modifications at desired times during rerecording without changing the pattern of said modifications, reproducing said rerecorded record of said waves, reproducing the changed record or said modifications, and controlling the reproduction of said waves by the changed record of said modifications to restore the amplitude variations of the original waves, and to enhance the amplitude variations in the reproduced waves.

. HARVEY FLETCHER. 

